Vinyl chloride interpolymer coating composition

ABSTRACT

A process for coating a material, e.g. a vinyl material, to improve its wear resistance and the coated article produced thereby is disclosed. The coating comprises an interpolymer comprising from about 50-95% by weight polyvinyl chloride and from about 5-50% by weight of an acrylate dissolved in an organic solvent.

This is a divisional application of U.S. Patent Application Ser. No.474,747, filed May 30, 1974, which is now U.S. Pat. No. 3,997,704.

TECHNICAL DESCRIPTION OF THE INVENTION

The present invention relates to a process for coating a material, e.g.a vinyl material, to improve its wear and/or weather resistance and thecoated article formed thereby. The coating composition used herein whenapplied in either the molten state or in solution to a variety of normalsensitive substrates protects them from abrasion. The process isparticularly directed to coating vinyl materials and will be describedin terms of this preferred embodiment. As used herein "vinyl material"is intended to include homopolymers of vinyl chloride and copolymers ofvinyl chloride with the other well-known monomers which copolymerizewell with vinyl chloride, e.g., vinyl acetate.

The composition which is coated upon the vinyl material comprises apolyvinyl chloride-acrylate interpolymer which comprises from about50-95% by weight polyvinyl chloride and 5-50% by weight of an acrylate.The polyvinyl chloride can be either a homo- or copolymer of vinylchloride as mentioned above in connection with the definition for "vinylmaterial".

As used herein, the term "interpolymer" indicates the product formed bypolymerizing an acrylate monomer in the presence of prepolymerized PVC.There is little or no grafting between the acrylate polymer and the PVC.The product is formed (1) by suspension polymerizing vinyl chlorideunder conditions whereby polyvinyl chloride is preferably obtained in acertain particle size range by means of a conventional, free radicalinitiated, suspension polymerization at a controlled rate of agitationand in the presence of a specified concentration of a suspending agent;(2) by removing unreacted vinyl chloride from the system afterpolymerization is at least 60% complete; (3) by then adding to thesystem an effective concentration of a chain transfer agent, a minorproportion, ie.e, up to about 50% by total solids weight, of an acrylateester monomer or mixture of acrylate ester monomers, as hereinafterdefined, and an initiator; (4) by continuing the polymerization untilthe thus added acrylate is polymerized in and/or on the particles of thepreviously polymerized PVC; and (5) by separating thepolyacrylate-modified polyvinyl chloride thereby obtained. Apparently,the thus added acrylate ester monomer is absorbed by the initiallyprepared polyvinyl chloride particles so as to thereby produce apolyacrylate-modified PVC resin which acts as an effective topcoat for avariety of materials, e.g. vinyl materials, after being applied to thematerial in the molten state or in an appropriate solvent as will bedescribed below. The polyacrylate-modified PVC resin used in thisinvention differs from the material described in Naps et al. U.S. Pat.No. 2,746,944 which is a graft polymer of acrylate on a preformed PVCbackbone rather than an interpolymer between the acrylate and PVCcontaining little or no grafting. It also differs from the materialdescribed in Bader et al. Pat. No. 3,551,372 which uses far largeramounts of acrylates than the amounts used herein in a differing coatingcomposition.

It has been found that the utilization of: (1) completely removing anyunreacted vinyl chloride monomer prior to introducing and initiating thepolymerization of the acrylate, (2) the addition of catalyst andacrylate as those steps are described in greater detail below, and (3)use of a chain transfer agent during the polymerization of the acrylatecombine to contribute towards the attainment of a polyacrylate-modifiedpolyvinyl chloride having excellent properties as a coating. Theseproperties appear to be directly attributable to the fact that themoieties derived from the acrylate and from any optional comonomerswhich may also be present in the system, can be consistently obtained bymeans of this process whereas such products cannot ordinarily beprepared under conditions where (1) the unreacted vinyl chloride is notremoved from the system; (2) the acrylate and catalyst are not added tothe suspension PVC medium as described in greater detail later and (3) achain transfer agent is not present in the system during thepolymerization of the acrylate and any optional comonomers.

Similarly, by controlling the rate of agitation and the concentration ofthe suspending agent that is present in the system during the initalpolymerization of the PVC as well as during the subsequentpolymerization of the acrylate ester monomer, it is possible to readilycontrol the size of the initially produced PVC particles, therebygreatly facilitating the absorption and the polymerization of thesubsequently introduced acrylate and any optional monomers. In the samemanner, the size of the resulting polyacrylate-modified polyvinylchloride particles is readily maintained within the required limits soas to avoid producing them in too large a particle size therebypreventing "gell", "fish-eye" or "grain-like" surface characteristics inthe final PVC coating composition formed from the particles produced bythe process described herein.

The acrylate component is introduced into the system in a concentrationof from about 5-50%, and preferably about 25-35%, by weight, of thepreviously polymerized PVC so that polyvinyl chloride comprises fromabout 50-95%, and preferably 65-75%, by weight, of the total weight ofthis product.

The acrylates which can be included in the acrylate portion are selectedfrom the group consisting of the C₁ -C₄ straight and branched alkylmethacrylates, e.g. methyl, ethyl, n-propyl and isopropyl methacrylate;the glycidyl esters of acrylic and methacrylic acid, e.g. glycidylmethacrylate and glycidyl acrylate; and, the C₁ -C₁₂ alkyl acrylateswherein the alkyl group may be straight or branched, e.g. methyl,n-propyl, n-butyl, isobutyl, tert-butyl, hexyl, 2-ethylhexyl, decyl anddodecyl acrylate; or any mixtures of these acrylate monomers. It ispreferred to use methyl methacrylate at 50% or above, by weight, in theacrylate component. If desired it can be the sole acrylate. Especiallypreferred is a polyacrylate modified PVC which comprises about 70-71%,by weight, of polyvinyl chloride and about 29-30% by weight of apolyacrylate ester moiety which in turn comprises a copolymer containingabout 86-93% by weight, of methyl methacrylate and 7-14% by weight, ofn-butyl acrylate.

The process for forming the particles comprises adding the appropriateamount of acrylate ester monomer, comprising, for instance, methylmethacrylate with or without one or more optional comonomers, to apreviously polymerized, aqueous suspension of polyvinyl chloride. Inconducting such a suspension polymerization process for the preparationof PVC, the vinyl chloride monomer, or a mixture of vinyl chloride witha minor proportion of an appropriate comonomer such as vinyl acetate ora lower alkyl acrylate, is admixed with a concentration of from about0.01 to 5.0%, as based on the weight of the total monomer mixture, of asuspending agent such, for example, as methyl cellulose, hydroxyethylcellulose, hydroxypropyl cellulose, carboxymethyl cellulose, talc, clay,polyvinyl alcohol, gelatine and the like. As has already been noted, theparticle size of the resulting PVC particles has been found to beaffected by the concentration of the suspending agent that is present inthe system. Thus, it is necessary to utilize a concentration of theselected suspending agent which is within the above stated limits. Forexample, if the latter maximum limit for the concentration of thesuspending agent is substantially exceeded, the resulting PVC particleswill be well below the required particle size range which, as will befurther discussed hereinbelow, is in the range of from about 5 to 150microns. Conversely, if the lower limit of this range is not met, theresulting PVC particles will be far too large.

In addition, a monomer soluble, free radical catalyst or initiator such,for example as 2,2'-azobisisobutyronitrile, lauroyl peroxide, benzoylperoxide or isopropylperoxy dicarbonate should be present in the systemin a concentration of from about 0.01 to 3%, by weight, of the totalmonomer charge being utilized for the polymerization of the PVC or vinylchloride copolymer.

Polymerization may then be initiated by heating the above-describedrecipe at a temperature in the range of from about 20 to 90° C. and fora period of from about 3 to 15 hours with agitation being appliedthroughout the course of the reaction. As was discussed hereinabove,with respect to the concentration of the suspending agent, the rate atwhich agitation is applied during the polymerization of the PVC is stillanother significant process variable which affects the particle size ofthe resulting PVC particles. Thus, if insufficient agitation is applied,the PVC particles will be far too large.

As will be understood by those skilled in the art, the substantialnumber of variations in the size and configuration of the agitationapparatus and reaction vessels which can be utilized in polymerizationprocesses makes it impossible to set forth a range for the rate ofagitation that is required to be applied in conducting thepolymerization of PVC. Accordingly, the agitation rate to be appliedunder any specific reaction conditions will be largely dependent uponsuch factors as the concentration of the suspending agent that ispresent in the system as well as on the design of the particularagitator, e.g. the shape of its blades, and reaction vessel, e.g. thenumber and design of its baffles, which are being utilized. Thus, theskill of the practitioner in the art will readily enable him to makewhatever adjustments may be necessary in order to prepare the resultingPVC particles so that they are all substantially within the above givenparticle size range of from about 5 to 150 microns and, preferably, fromabout 25 to 80 microns.

The size of these PVC particles is an important feature of thisinvention. The reason is not entirely understood, but apparently theacrylate ester monomer, i.e., methyl methacrylate and any optionalmonomers, is somehow improperly absorbed by PVC particles which aresubstantially larger than the above stated maximum of 150 microns and itcannot, therefore, be effectively polymerized.

Similarly, as has already been noted, it is necessary that the particlesize of the final product, i.e, of the polyacrylate-modified polyvinylchloride particles, be within certain limits. Thus, it is necessary thatthey should range in size from a minimum of about 10 microns up to amaximum limit such that no more than about 15%, be weight, are largerthan about 150 microns. A preferred range is from about 40 to 150microns. Thus, if the particles are substantially smaller than thelatter minimum size, it will be extremely difficult to isolate them withconventional plant equipment. Conversely, if the maximum limit for thesize of these processing aid particles is substantially exceeded,"gells", "fish-eye", and the above described "applesauce" effect will beimparted to the coating containing such oversized particles.

Polymerization of the subsequently added acrylate ester monomer isinitiated by at least one standard monomer soluble, i.e, oil-soluble,free radical initiating catalyst. Suitable catalysts include,2,2'-azobisisobutyronitrile, lauroyl perioxide, benzoyl peroxide,t-butyl peroxypivalate and isopropylperoxy dicarbonate. The catalyst caneither be premixed with the acrylate prior to addition to the warmsuspension PVC medium, as described in Kraft et al. U.S. Pat. No.3,928,500 or by addition of both acrylate and non-premixed catalyst tothe PVC suspension when the latter is cool as described in Dyer et al.U.S. Pat. No. 3,919,137 followed by application of heat to thesuspension medium. The former procedure for adding acrylate andinitiator is the preferred method. Processes for forming the type ofinterpolymers used in the present invention are described and claimed inthese applications.

Chain transfer agents are used during the polymerization of the acrylateand any optional monomers, in order to further control the finalproperties of the resulting acrylate modified PVC particles. These chaintransfer agents, can be selected from the group consisting of:

1. chlorinated aliphatic hydrocarbons such as carbon tetrachloride,chloroform, methylene chloride, butyl chloride, methyl chloroform,propylene chloride and trichloroethylene;

2. aromatic hydrocarbons such as toluene, xylene, mesitylene, cumene,ethyl benzene, t-butyl benzene and chlorobenzene;

3. aldehydes such as acetaldehyde, propionaldehyde, benzaldehyde andcrotonaldehyde;

4. aliphatic and cyclic ketones such as methyl ethyl ketone, acetone,diethyl ketone, methyl isobutyl ketone and cyclohexanone methyl ethylketone;

5. cyclic ethers such as dioxane and tetrahydrofuran;

6. alkyl esters of aliphatic carboxylic acids such as methyl isobutyrateand ethyl acetate;

7. aliphatic alcohols such as sec-butyl alcohol, n-butyl alcohol,isobutyl alcohol and t-butyl alcohol;

8. aliphatic carboxylic acids such as acetic acid;

9. cyclic hydrocarbons such as methyl cyclohexane; and, most preferably

10. mono- di- and polymercaptans including monomercaptans such as methylmercaptan; ethyl mercaptan; propyl mercaptan; n-butyl mercaptan; n- andt-butyl mercaptan; n- and t-phentyl mercaptan; hexyl mercaptan; n- andt-heptyl mercaptan; n- and t-octylmercaptan; n- and t-decyl mercaptan;n-dodecyl, i.e., lauryl, and t-dodecyl mercaptan; n- and t-octadecylmercaptan; n- and t-cicosyl mercaptan; n- and t-pentacosyl mercaptan; n-and t-octacosyl mercaptan; n- and t-triconyl mercaptan and blendsthereof. From this group of mono-mercaptans, it is preferred to uselauryl mercaptan.

Other operable monomercaptans include thiocetic acid;1-mercapto-2-butanone; methyl mercaptoacetate; ethylmercaptothioacetate; 1-mercapto-2-ethoxyethane; diethyl mercaptoethylphosphorotrithioate; 2-mercaptoethyl acetamide; dimethyl aminomethylmercaptan; cysteamine; mercaptomethylthiopropane;monomercaptocyclohexane; benzyl mercaptan; cysteine; and,mercaptoethnol.

Suitable dimercaptan chain transfer agents can be illustrated byethanedithiol; 2,3 dimercaptopropanol; decanedithol-1,10 and the like.

Suitable polymercaptan chain transfer agents having more than 3mercaptan groups per molecule can be illustrated by pentaerythritoltetra (7-mercaptoheptanoate); mercaptoacetic acid triglyceride;pentaerythritol tri(beta-mercaptopropionate); pentaerythritoltetra(beta-mercaptopropionate); cellulose tri(alphamercaptoacetate);1,2,3-propane-trithiol, 1,2,3,4-neopentane tetrathiol;1,2,3,4,5,6-mercaptopoly(ethyleneoxy)ethyl(sorbitol); 1,1,1-trimethylpropane tri(alpha-mercaptoacetate); dipentaerythritolhexa(3-mercaptopropionate); 1,2,3-tris(alpha-mercaptoacetypropane;thiopentaerythritol tetra(alpha-mercaptoacetate;,1,6,10-trimercaptocyclododecane, 1,2,3,4,5,6-hexamercaptocyclohexane;N,N', N"N'"-tetra(2-mercaptoethyl)pyromellitamide;tri-(2-mercaptoethyl)nitriolotriacetate; pentaerythritoltri(alpha-mercaptoacetate); pentaerythritoltetra(alpha-mercaptoacetate); tri(p-mercaptomethylphenyl)methane;2,2,7,7-tetrakis(mercaptomethyl) -4,5 dimercapto-octane;5,5,5-tri(mercaptoethyl)phosphorotrithioate; xylitolpenta(beta-mercaptopropionate); and, the like.

Illustrative of low molecular weight polymeric materials having at least3 pendant mercaptan groups per molecule are homopolymers and copolymersof vinyl thiol, e.g., polyvinyl thiol. Other polymeric thiols, such asglycerol/ethylene glycol polyether polymercaptan can also be used aschain transfer agents in forming the particles to be used in thecoating.

From the above group, optimum results are, however obtained by the useof low molecular weight polymercaptans having from 3,5 mercaptan groupsper molecule as illustrated by pentaerythritol tetrathioglycolate;pentaerythritol tetra(3-mercaptopropionate); trimethylolethanetri(3-mercaptopropionate); xylitol penta(beta-mercaptopropionate);trimethylolethane trithioglycolate trimethylolpropanetri(3-mercaptopropionate); and, trimethylolpropane trithioglycolate. Theuse of the latter polymercaptans are preferred since they are mostefficient with respect to the reate of polymerization which isattainable in the system wherein they are utilized.

With respect to the amount of chain transfer agent used in the processof this invention, this will largely be determined by the particularchain transfer agent that is selected. However, in most instances theymay be utilized in a concentration of from about 0.025-7.5%, as based onthe total weight of the acrylate ester monomer charge. In general,mercaptans, and particularly polymercaptans, are more efficient and maybe used in concentrations at the lower end of the latter range whereasless efficient chain transfer agents, such as the aromatic hydrocarbons,will be used in concentrations at the upper end of this range.

By utilizing a chain transfer agent, it is possible to exercise agreater degree of control upon the molecular weight, i.e., to preventthe attainment of a molecular weight which is higher than the maximumvalue in the below stated range, of that portion of the final polymericproduct which is derived from the acrylate. This, in turn, affects themolecular weight of the product as a whole. Thus, it may be here statedthat the products resulting from the process should, preferably, have amolecular weight, as expressed in terms of their Relative Viscosity, asdetermined in a 1%, by weight, solution of the polymer in cyclohexanoneat 25° C, of from about 1.50-2.80 and, preferably, from about 2.30-2.60.Thus, it has been found that those products having a Relative Viscositywithin this range will display the desired characteristics whenincorporated in a coating on the vinyl material. As is known to thoseskilled in the art, Relative Viscosity is calculated by the use of thefollowing formula:

    Relative Viscosity=T.sub.1 /R.sub.2

where T₁ = the time required for the passage of a standard volume of thepolymer solution through an orifice in a viscometer and T₂ = the timerequired for the passage of a standard volume of the solvent through theorifice in the identical viscometer.

The polymerization of the acrylate ester monomer is conducted by heatingthe system, i.e., the selected chain transfer agent, the previouslyprepared PVC host polymer and the mixture of the catalyst with theacrylate ester monomer, at a temperature of from about 40° to 100° C.for a time sufficient to completely polymerize the acrylate estermonomer in and/or on the host PVC particles. It is to be pointed outthat it is not ordinarily necessary to introduce any fresh suspendingagent into the system since a sufficient quantity will already bepresent from the initial polymerization of the PVC.

The particular catalyst, temperature, reaction time and other operatingconditions chosen are, of course, interdependent and may be thoseordinarily employed in the polymerization of MMA. Other variations inpolymerzation technique will suggest themselves to those skilled in theart.

The process of this invention is particularly satisfactory whenconducted with polyvinyl chloride homopolymers as the initially preparedvinyl chloride host polymer. However, as has already been briefly noted,there can also be employed the usual copolymers of vinyl chloride withminor proportions of one or more ethylenically unsaturated, i.e., vinyl,comonomers provided that the resulting vinyl chloride copolymers arewithin the above specified particle size and Relative Viscosity ranges.

Illustrative of these vinyl comonomers which can be used in preparingeither the vinyl chloride host polymer of the coating composition ofthis invention or the vinyl chloride polymer material upon which thesecoating compositions may be placed include alpha-olefins such asethylene, propylene and butylene; vinyl esters of carboxylic acids suchas vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl stearate;C₁ -C₂₀ alkyl esters of acrylic and methacrylic acid such as methylmethacrylate, methyl acrylate, ethyl acrylate, butyl acrylate,2-ethylhexyl acrylate and lauryl acrylate; aryl, halo- and mitro-substituted benzyl esters of acrylic and methacrylic acid such as benzylacrylate and 2-chlorobenzyl acrylate; ethylenically unsaturatedmonocarboxylic acids such as acrylic and methacrylic acids;ethylenically unsaturated dicarboxylic acids, their anhydrides and theirC₁ 14 C₂₀ mono- and dialkyl esters such as aconitic acid, fumaric acid,maleic acid, itaconic acid, citraconic acid, maleic anhydride, dibutylfumarate and mono-diethyl maleate; amides of ethylenically unsaturatedcarboxylic acids such as acrylamide and methacrylamide; vinyl arylcompounds such as styrene and alpha-methyl styrene; nitriles ofethylenically unsaturated carboxylic acids such as acrylonitrile andmethacrylonitrile; vinyl pyrrolidones such as N-vinyl-2-pyrrolidone; C₁-C₂₀ alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl etherand stearyl vinyl ether; dienes such as isoprene and butadiene; and,glycidyl esters of acrylic and methacrylic acid such as glycidylacrylate and glycidyl methacrylate, etc.

The polyvinyl chloride-acrylate particles when formed can be applied tothe vinyl material as a coating by any means known to the art, e.g.,knife coating, roller coating and spray coating of a solution or byapplying them in the molten state. The resin particles are preferablyfirst dissolved in a suitable organic solvent, e.g. ketones such asmethyl ethyl ketone, tetrahydrofuran, methyl isobutyl ketone, acetone,cyclohexanone or mixtures thereof in an amount ranging from 5% to 35%,by weight, preferably 10% to 20%. It is well within the skill of aperson in the art to adjust the amount of solvent to give the bestresults with the particular application that is chosen. This solution isthen added to the surface of the vinyl material in an amount rangingfrom 0.05 mil to 3.0 mil, preferably 0.2 - 0.5 mil.

The invention is further illustrated by the following Examples:

EXAMPLE I

This example illustrates the preparation of one of the preferredpolyacrylate-modified PVC interpolymers used in this invention.

Part 1

A 20 gallon Pfaudler reactor is charged with a standard recipe, as givenbelow for preparing suspension grade polyvinyl chloride. Thepolymerization is conducted at 60° C. for 51/2 hours, with agitationbeing applied at a rate of about 300 rpm, resulting in the preparationof PVC particles having an average particle size of about 25-30 microns:

    ______________________________________                                                         Parts                                                        ______________________________________                                        Vinyl Chloride     221                                                        Water              234                                                        Methyl Cellulose    50 (1% aqueous solution)                                  2,2'-azobisisobuty-                                                           ronitrile (Catalyst)                                                                             0.144                                                      ______________________________________                                    

Part 2

When the reaction of Part 1, hereinabove, is essentially complete, i.e.,about 80-85% conversion, all of the excess vinyl chloride monomer isvented off whereupon 0.027 parts of lauryl mercaptan chain transferagent followed by a mixture of 93 parts of methyl methacrylate, i.e.,MMA, and 7 parts of n-butyl acrylate which has first been pre-mixed with0.063 parts of additional 2,2'-azobisisobutyronitrile catalyst, areadded. Under agitation at a rate of 300 rpm, the polymerization isallowed to proceed for about 5 hours at 75° C. until the MMA ispolymerized in and/or on the host PVC particles. The resulting resinproduct, which comprises particles containing about 70%, by weight, ofPVC and about 30%, by weight, of a polyacrylate moiety comprising aboutan 93:7 methyl methacrylate:n-butyl acrylate copolymer, has a RelativeViscosity as determined under the conditions described hereinabove, ofabout 2.50. The particle size of this polyacrylate-modified PVC resin issuch that no more than about 10.1%, by weight, is larger than about 150microns.

EXAMPLE II

The resin from Example I was dissolved in methyl ethyl ketone so thatthe solution comprises about 85% by weight methyl ethyl ketone and 15%by weight resin. It was added to the cold solvent by slow sifting withstirring. When addition was completed, the temperature was raised to140° F to hasten solubilization. When the resin was totally solubilizedthe solution was cooled to room temperature and was ready for coatingoperations.

The resin was applied by a wire wound rod, and the coated vinyl wasdried at 270° F for 21/2 minutes in a forced air drying oven. Duringthis period the solvent evaporated from the resin solution leaving aclear continuous resin film.

EXAMPLE III

Two coated articles similar to that produced in Example II were testedfor wear properties using the Wyzenbeck wear test. This test utilizes a-8 Duck material which rubs the surface of the vinyl. The rubbing takesplace with a 3 lb. pressure of the abradant duck material against thecoated vinyl and a 4 lb. tension on the duck material. The results fortwo different film thicknessess utilizing two different number ofcycles:

    ______________________________________                                        Film Thickness                                                                            No. of Cycles Results                                             ______________________________________                                        0.24 mil     50,000       20% color transfer*                                 0.60 mil    100,000       Very slight color                                                             transfer                                            ______________________________________                                         *Indicates color transfer of pigment in the vinyl substrate to the            abradant material.                                                       

EXAMPLE IV

The stain resistance and cleanability of a coated vinyl article wereexamined. Common household articles, e.g., mustard, ketsup, lipstick,oil and water based inks were used to stain the coated vinyl. The stainswere allowed to stand on the coated vinyl for 18 hours at 72° F and 50%relative humidity. After this period they were washed with mild soap andwarm water and the degree of staining which remained on the vinyl wasnoted. All stains were slight and readily were washed off with littleresistance. Only the mustard and oil based ink stains remained.

EXAMPLE V

The coated vinyl was exposed to ultraviolet radiation for four weeks inan American Cyanamid Test Cabinet (Fadeometer) FBSL containingfluorescent, blacklight and sunlamps. No discoloration or loss offlexibility was found. Ordinarily merely 200 hours or over exposure withthese results would be considered acceptable.

The coating of the present invention has a wear resistance that is asgood as commerically used polyvinyl chlorideacrylic blend coatings buthas superior weather resistance and is less costly.

What is claimed is:
 1. A coating composition adapted to be used to coata material which comprises (a) an organic solvent, and (b) aninterpolymer formed by polymerizing an acrylate in the presence of avinyl chloride containing polymer formed by suspension polymerization,said interpolymer containing from about 50% to 95%, by weight, vinylchloride polymer and from about 5% to 50%, by weight, of an acrylate,said vinyl chloride containing polymer having a particle size of fromabout 5 to about 150 microns.
 2. A composition as claimed in claim 1wherein the interpolymer comprises about 65-75% by weight polyvinylchloride.
 3. A composition as claimed in claim 1 wherein theinterpolymer comprises about 25-35% by weight of the acrylate.
 4. Acomposition as claimed in claim 1 wherein the acrylate is selected fromthe group consisting of the C₁ -C₄ alkyl methacrylates, the glycidylesters of acrylic and methacrylic acid, and the C₁ 14 C₁₂ alkylacrylates.
 5. A composition as claimed in claim 1 wherein methylmethacrylate comprises greater than about 50% by weight of the acrylate.6. A composition as claimed in claim 1 wherein the acrylate comprisesabout 86-93% by weight methyl methacrylate and about 7-14% by weightn-butyl acrylate.
 7. A composition as claimed in claim 1 wherein thecoating composition comprises from about 5% to 35% by weight of theinterpolymer.
 8. A composition as claimed in claim 1 wherein the organicsolvent is selected from the group consisting of methyl ethyl ketone,methyl isobutyl ketone, acetone, cyclohexanone, tetrahydrofuran andmixtures thereof.
 9. A composition as claimed in claim 1 wherein theinterpolymer has a particle size of from about 10 microns to a maximumvalue wherein not more than about 15% by weight are larger than about150 microns.
 10. A composition as claimed in claim 1 wherein theinterpolymer is present at from 10% to 20%.